295 

 employing this novel reagent gas. This appendix provides the fundamental 

 background for future work of this nature with optimization related to that on the 

 TSQ70 triple quadrupole mass spectrometer. 



High Pressure Charge Exchange Mass Spectrometry 



The main use of CO2 as a reagent gas has been in the analysis of positive ions 

 [33,74]. This reagent gas functions in positive ion mode as a medium for charge 

 exchange. Unlike reagent gases employed for work in this dissertation (i.e. methane 

 and isobutane), carbon dioxide does not contain a hydrogen for proton transfer 

 reactions. Therefore, only hydride (or heavier ion) transfer, electron transfer, or 

 adduct formation are viable routes for the production of positively charged sample 

 ions [33,74,112]. Charge exchange (see Chapter 5 for additional information) occurs 

 by electron ionization of the reagent gas, with subsequent transfer of the positive 

 charge from reagent gas to sample molecules via collisions. The resultant deposition 

 of internal energy (Ej) from these collisions is given by: 



E; = RE(X*') - IE(M) A-1 



where RE (X*') is the recombination energy of the reagent gas ion, X"^', and IE (M) 

 is the ionization energy of the sample molecule, M. The recombination energy for 

 COz"^' is 13.8 eV [74,113]. Extensive fragmentation occurs for a high value of E^. 

 If RE (X"^*) is only slightly greater than IE (M), then the mass spectrum is expected 

 to contain predominantly the M*' ion. 



